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From: Paul E. McKenney on 4 Aug 2010 20:50 On Wed, Aug 04, 2010 at 05:25:53PM -0700, david(a)lang.hm wrote: > On Wed, 4 Aug 2010, Paul E. McKenney wrote: > > >On Wed, Aug 04, 2010 at 04:49:22PM -0700, david(a)lang.hm wrote: > >>On Wed, 4 Aug 2010, Paul E. McKenney wrote: > >> > >>>On Wed, Aug 04, 2010 at 04:23:43PM -0700, david(a)lang.hm wrote: > >>>>On Wed, 4 Aug 2010, Arve Hj?nnev?g wrote: > >>>> > >>>>> > >>>>>We suspend as soon as no wakelocks are held. There is no delay. > >>>> > >>>>So, if I have a bookreader app that is not allowed to get the > >>>>wakelock, and nothing else is running, the system will suspend > >>>>immediatly after I click a button to go to the next page? it will > >>>>not stay awake to give me a chance to read the page at all? > >>>> > >>>>how can any application run without wakelock privilages? > >>> > >>>Isn't a wakelock held as long as the display is lit, so that the > >>>system would continue running as long as the page was visible? > >> > >>what holds this wakelock, and what sort of timeout does it have? > >>(and why could that same timeout be used in other ways instead) > > > >I defer to the Android guys on what exactly holds the display's > >wakelock. The timeout is the display-blank timeout. > > > >>how many apps really need to keep running after the screen blanks? > >>there are a few (audio output apps, including music player and > >>Navigation directions), but I don't have see a problem with them > >>being marked as the 'trusted' apps to pay attention instead. > > > >Downloading is another. > > this is definantly an interesting case, do you want an active > network connection to keep the machine awake? if so do you want it > for all network connections, or only for some... The Android approach is that everything is permitted to run when the device is not suspended. So that would be all network connections. > >The music player is an interesting example. It would be idle most > >of the time, given that audio output doesn't consume very much CPU. > >So you would not want to suspend the system just because there were > >no runnable processes. In contrast, allowing the music player to > >hold a wake lock lets the system know that it would not be appropriate > >to suspend. > > > >Or am I misunderstanding what you are proposing? > > the system would need to be idle for 'long enough' (configurable) > before deciding to suspend, so as long as 'long enough' is longer > than the music player is idle this would not be a problem. From a user standpoint, having the music player tell the system when it is OK to suspend (e.g., when the user has paused playback) seems a lot nicer than having configurable timeouts that need tweaking. > >>if the backlight being on holds the wakelock, it would seem that > >>almost every other use of the wakelock could (and probably should) > >>be replaced by something that tickles the display to stay on longer. > > > >The problem with this approach is that the display consumes quite a > >bit of power, so you don't want to leave it on unnecessarily. So if > >the system is doing something (for example, playing music) that does > >not require the display, you really want the display to be off. > > what percentage (and types) of apps are really useful with the > display off. I think that there are relativly few apps that you > really want to keep running if the display is off. The length of time those apps are running is the governing factor for battery life, and not the number of such apps, right? Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Arve Hjønnevåg on 4 Aug 2010 21:10 2010/8/4 Rafael J. Wysocki <rjw(a)sisk.pl>: > On Thursday, August 05, 2010, Arve Hj�nnev�g wrote: >> On Wed, Aug 4, 2010 at 1:56 PM, Matthew Garrett <mjg59(a)srcf.ucam.org> wrote: >> > On Wed, Aug 04, 2010 at 10:51:07PM +0200, Rafael J. Wysocki wrote: >> >> On Wednesday, August 04, 2010, Matthew Garrett wrote: >> >> > No! And that's precisely the issue. Android's existing behaviour could >> >> > be entirely implemented in the form of binary that manually triggers >> >> > suspend when (a) the screen is off and (b) no userspace applications >> >> > have indicated that the system shouldn't sleep, except for the wakeup >> >> > event race. Imagine the following: >> >> > >> >> > 1) The policy timeout is about to expire. No applications are holding >> >> > wakelocks. The system will suspend providing nothing takes a wakelock. >> >> > 2) A network packet arrives indicating an incoming SIP call >> >> > 3) The VOIP application takes a wakelock and prevents the phone from >> >> > suspending while the call is in progress >> >> > >> >> > What stops the system going to sleep between (2) and (3)? cgroups don't, >> >> > because the voip app is an otherwise untrusted application that you've >> >> > just told the scheduler to ignore. >> >> >> >> I _think_ you can use the just-merged /sys/power/wakeup_count mechanism to >> >> avoid the race (if pm_wakeup_event() is called at 2)). >> > >> > Yes, I think that solves the problem. The only question then is whether >> >> How? By passing a timeout to pm_wakeup_event when the network driver >> gets the packet or by passing 0. If you pass a timeout it is the same >> as using a wakelock with a timeout and should work (assuming the >> timeout you picked is long enough). If you don't pass a timeout it >> does not work, since the packet may not be visible to user-space yet. > > Alternatively, pm_stay_awake() / pm_relax() can be used. > Which makes the driver and/or network stack changes identical to using wakelocks, right? >> > it's preferable to use cgroups or suspend fully, which is pretty much up >> > to the implementation. In other words, is there a reason we're still >> >> I have seen no proposed way to use cgroups that will work. If you >> leave some processes running while other processes are frozen you run >> into problems when a frozen process holds a resource that a running >> process needs. >> >> >> > having this conversation? :) It'd be good to have some feedback from >> > Google as to whether this satisfies their functional requirements. >> > >> >> That is "this"? The merged code? If so, no it does not satisfy our >> requirements. The in kernel api, while offering similar functionality >> to the wakelock interface, does not use any handles which makes it >> impossible to get reasonable stats (You don't know which pm_stay_awake >> request pm_relax is reverting). > > Why is that a problem (out of curiosity)? > Not having stats or not knowing what pm_relax is undoing? We need stats to be able to debug the system. If the system does not suspend at all or is awake for too long, the wakelock stats tells us which component is at fault. Since pm_stay_awake and pm_relax does not operate on a handle, you cannot determine how long it prevented suspend for. >> The proposed in user-space interface >> of calling into every process that receives wakeup events before every >> suspend call > > Well, �you don't really need to do that. > Only if the driver blocks suspend until user-space has read the event. This means that for android to work we need to block suspend when input events are not processed, but a system using your scheme needs a pm_wakeup_event call when the input event is queued. How to you switch between them? Do we add separate ioctls in the input device to enable each scheme? If someone has a single threaded user space power manager that also reads input event it will deadlock if you block suspend until it reads the input events since you block when reading the wake count. >> is also not compatible with existing apps. > > Thanks, > Rafael > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo(a)vger.kernel.org > More majordomo info at �http://vger.kernel.org/majordomo-info.html > Please read the FAQ at �http://www.tux.org/lkml/ > -- Arve Hj�nnev�g -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Matt Helsley on 4 Aug 2010 22:00 On Wed, Aug 04, 2010 at 05:35:09PM +0100, Matthew Garrett wrote: > On Wed, Aug 04, 2010 at 09:32:16AM -0700, Paul E. McKenney wrote: > > > If this doesn't work for the Android folks for whatever reason, another > > approach would be to do the freeze in user code, which could track > > whether any user-level resources (pthread mutexes, SysV semas, whatever) > > where held, and do the freeze on a thread-by-thread basis within each > > "victim" application as the threads reach safe points. > > The main problem I see with the cgroups solution is that it doesn't seem > to do anything to handle avoiding loss of wakeup events. cgroups alone don't but there is a solution which doesn't require routing all event data through a single server -- use SIGIO. Suppose we've got two cgroups of tasks -- those in the initial freezer cgroup and those in a freezer cgroup meant for power-naive apps. Let's call the second cgroup the naive cgroup. One task -- let's call it the "waker" -- is in the initial cgroup is normaly asleep waiting for SIGIO. Note it's not an "app" -- it's been trusted/blessed to be a non-power-naive task. It will be signaled via SIGIO by the applications which want to be unfrozen when an event comes in. When the power-naive app in the naive cgroup opens a file descriptor it's going through the Android interpretter to make the syscall. The interpretter can do fcntl() on the fd to cause SIGIO to be delivered to the waker task. When the waker gets SIGIO it unfreezes the naive cgroup and thus wakes the power-naive app. When the power-naive app wakes it will poll/return-from-poll/read/return-from-read and thus retrieve the event. Then it's just a matter of choosing when to freeze the naive cgroup. That requires a userspace implementation of the suspend blockers API plus opportunistic suspend but does not require any other kernel pieces. Then you can use sigprocmask to prevent the freeze/wake-event race. You would probably even merge the waker with the daemon which implements opportunistic suspend. Cheers, -Matt Helsley -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Brian Swetland on 4 Aug 2010 22:10 On Wed, Aug 4, 2010 at 6:58 PM, Matt Helsley <matthltc(a)us.ibm.com> wrote: > On Wed, Aug 04, 2010 at 05:35:09PM +0100, Matthew Garrett wrote: >> >> The main problem I see with the cgroups solution is that it doesn't seem >> to do anything to handle avoiding loss of wakeup events. > > cgroups alone don't but there is a solution which doesn't require routing > all event data through a single server -- use SIGIO. > > Suppose we've got two cgroups of tasks -- those in the initial freezer > cgroup and those in a freezer cgroup meant for power-naive apps. Let's > call the second cgroup the naive cgroup. > > One task -- let's call it the "waker" -- is in the initial cgroup is normaly > asleep waiting for SIGIO. Note it's not an "app" -- it's been trusted/blessed > to be a non-power-naive task. It will be signaled via SIGIO by the > applications which want to be unfrozen when an event comes in. > > When the power-naive app in the naive cgroup opens a file descriptor it's > going through the Android interpretter to make the syscall. The interpretter > can do fcntl() on the fd to cause SIGIO to be delivered to the waker task. > When the waker gets SIGIO it unfreezes the naive cgroup and thus wakes the > power-naive app. When the power-naive app wakes it will > poll/return-from-poll/read/return-from-read and thus retrieve the event. The Android execution model includes native code in addition to the dalvik VM, and in the future could include other runtimes -- there are many standard libraries that directly make posix file IO calls, and apps can bundle native libraries which can also directly make syscalls. It's not practical to instrument every piece of userspace code that opens a fd somehow to make additional fcntl calls in various places. Brian -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Paul E. McKenney on 4 Aug 2010 22:50
On Wed, Aug 04, 2010 at 03:08:33PM -0700, Arve Hj�nnev�g wrote: > On Wed, Aug 4, 2010 at 1:56 PM, Matthew Garrett <mjg59(a)srcf.ucam.org> wrote: [ . . . ] > > having this conversation? :) It'd be good to have some feedback from > > Google as to whether this satisfies their functional requirements. > > That is "this"? The merged code? If so, no it does not satisfy our > requirements. The in kernel api, while offering similar functionality > to the wakelock interface, does not use any handles which makes it > impossible to get reasonable stats (You don't know which pm_stay_awake > request pm_relax is reverting). The proposed in user-space interface > of calling into every process that receives wakeup events before every > suspend call is also not compatible with existing apps. I should have asked this earlier... What exactly are the apps' compatibility constraints? Source-level APIs? Byte-code class-library invocations? C/C++ dynamic linking? C/C++ static linking (in other words, syscall)? Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |